Microporous membranes with diverse properties are used in many modern products, including such things as filters, breathable articles, absorbent articles, and medical articles. There are many known ways to manufacture microporous membranes, including inducing a phase inversion in a dope layer. By manipulating the conditions that trigger the phase inversion, different morphologies can be generated in the resulting microporous membrane, adapting it to the specific needs of the end user.
One of the ways that a phase inversion can be triggered is by contacting a dope formulation with a coagulant. Methods of making microporous membranes are further described in U.S. Pat. No. 6,736,971 (Sale et al.); U.S. Pat. No. 5,869,174 (Wang); U.S. Pat. No. 6,632,850 (Hughes et al.); U.S. Pat. No. 4,992,221 (Malon et al.); U.S. Pat. No. 6,596,167 (Ji et al.); U.S. Pat. No. 5,510,421 (Dennis et al.); U.S. Pat. No. 5,476,665 (Dennison et al.); and U.S. Patent Application Publication Nos. 2003/0209485; 2004/0084364 (Kools).
One known way to introduce a coagulant to a dope layer is in the form of a vapor. It is also known to coagulate the dope layer, where the dope layer is moved through a coagulation bath. The bath would normally be constantly changing in concentration and purity as material diffuses into and out of the dope layer.